Honeywell Lycoming 700 Topping Check

[wheatbix]

Hello all,

We are reading up about the topping check required on the Lycoming 700 as installed in an AS350 SD2.

The check requires the installation of the spacer to limit Ng by 6%, then to go flying and hold 94% torque (or other MCP limit) in the climb at 55 knots until a rotor droop is experienced.

The manual reads as follows:

(2) Continue climbing at MCP (94% torque) until the set rotor speed cannot be
maintained and rotor RPM begins to droop. Do not allow rotor to droop below
375 RPM
NOTE
If due to low outside air temperature, altitude is
excessive increase gross weight as required but
not to exceed 4600 lb. (2086.5 kg)

My question is related to the note to add weight if the altitude becomes excessive.

Assuming the engine power is constant at whichever MCP limit, in my mind adding weight should only retard the rate of climb independant of the engine parameters. At the end of the day shouldnt the engine still droop at the same altitude, albeit a longer time to climb to that height?

[Gordy]

Forgive my "layman" answer---I am a pilot not a mathematician or engineer, and I could be wrong---I do it all by feel...

Lift = Weight

thrust = Drag

More weight means you need more lift ergo more power to get off the ground, therefore a higher power setting and you will reach the altitude that your RPM's start to droop sooner.....

[Gemini Twin]

That's correct Gordy. But perhaps more important is to make sure the max stop is screwed out fully before you install the spacer. Especially is you are installing an engine with an FCU that has been overhauled, as it will be delivered with bench spec flow settings. This will almost always the topping requirements are achieved on a single flight.